AUDITORY REPRESENTATIONS OF OPTIMISED CHIRP SIGNALS

Optimised chirp signals for ABR, recently suggested by Dau et al. (1998) have been tested with the Auditory Image Model (AIM, Patterson et al., 1995). AIM is a comprehensive model of the peripheral auditory system, including a stage of strobed temporal integration to produce a stabilised image of repeating neural activity patterns. The chirps are calculated to compensate for spatial dispersion along the cochlea in order to stimulate all auditory nerve fibres at the same moment in time. Outputs of the several stages of the model in response to the chirps illustrate the form that the internal representation of these signals might take. Both a linear gammatone filterbank, and a transmission line model of basilar membrane motion produce responses that are reasonably consistent with what would be expected from the chirp signals, i.e., a distinct alignment of cochlear excitation over time. At the higher stages of auditory processing, some of the intended alignment seems to get degraded. The auditory images of upward and downward sweeps show less asymmetry than would be expected from the excitation along the cochlea.